Fix push cancellation error dialog

[epeicher]

Related issues

• Fixes STU-1087

Proposed Changes

• Use .includes('Export aborted') instead of === 'Export aborted' when checking for push cancellation errors in the renderer process.
• Electron IPC wraps error messages as "Error invoking remote method '...': Error: <message>", so the strict equality check never matched the wrapped message. This caused cancelling a push during the export phase to show an error dialog and report to Sentry, instead of gracefully handling the cancellation.
• This is consistent with other IPC error checks in the codebase (e.g., use-site-details.tsx uses .includes() for the same reason).

Testing Instructions

1. Connect a local site to a WordPress.com site
2. Start a Push operation
3. Immediately cancel the push while it's in the "Creating backup" (export) phase
4. Verify that the push is cancelled gracefully with a "Push cancelled" notification — no error dialog should appear

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing a17aa0b vs trunk

site-editor

Metric	trunk	a17aa0b	Diff	Change
load	1440.00 ms	1468.00 ms	+28.00 ms	⚪ 0.0%

site-startup

Metric	trunk	a17aa0b	Diff	Change
siteCreation	7122.00 ms	7094.00 ms	-28.00 ms	⚪ 0.0%
siteStartup	3958.00 ms	4911.00 ms	+953.00 ms	🔴 24.1%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[bcotrim]

Works as described
LGTM 👍

[katinthehatsite]

This worked as expected for me 👍